1. FIELD OF THE INVENTION
The present invention relates to a disc driving unit, and more particularly to a disc driving unit that has a spindle for rotating a magnetic disc or similar disc member.
2. DESCRIPTION OF THE PRIOR ART
In general, a disc driving unit such as a magnetic disc driving unit applied to a magnetic disc apparatus for recording and/or reproducing an information on and/or from a magnetic disc as a magnetic recording medium has a spindle for rotating a disc member, a pulley connected to this spindle for transmission of a rotating force and a bearing which rotatably supports the spindle.
FIG. 1 shows an example of a conventional magnetic disc driving unit. In FIG. 1, reference numeral 1 denotes a base of the magnetic disc apparatus. The base 1 has a recess portion 1a formed with into a shape of a deep plate and a cylindrical portion 1b connecting with a bottom of the recess portion 1a.
A spindle 2 is rotatably disposed in the recess portion 1a, and clamps a magnetic disc (not shown) with a member such as a center cone. A shaft 2b of the spindle 2 is rotatably supported by the cylindrical portion 1b through bearing 3a and 3b.
A round recess 2a is formed on the upper edge of the spindle 2.
The bearing 3a and 3b are formed as ball bearings holding steel balls between their outer and inner rings. The upper side bearing 3a is fixed to the cylindrical portion 1b of the base 1 by press fitting or adhering the outer ring to the portion positioned by a cir-clip or a retaining ring 5 which is inserted into the groove 1c formed on the inside surface of the cylindrical portion 1b. The outer ring of the lower bearing 3b is attached to the cylindrical portion 1b so as to move up and down with an extremely small clearance with respect to the cylindrical portion 1b.
In the space between the upper and lower bearings 3a and 3b are disposed a spacer 6 and a belleville spring 7.
Reference numeral 4 denotes a pulley for transmitting a rotation to the spindle 2. The pulley 4 has a recess 4a and the cylindrical portion 1b is positioned in the recess 4a. The pulley 4 has a boss 4b that couples with the inner ring of the bearing 3b in the central portion of the recess 4a.
A screw 9 is attached to this boss 4b. The screw 9 screws into the shaft 2b of the spindle 2 so that the spindle 2 and the pulley 4 are formed into a single integrated structure.
Reference numeral 8 denotes a belt, which forms a connection between a drive source not shown and the pulley 4 so as to transmit a rotation.
The screw 9 aligns the center of rotation of the spindle 2 and the pulley 4. The bearing 3b is positioned through the spacer 6 and is applied an initial pressure by the belleville spring 7 so that a gap in the diametrical direction of the bearings 3a and 3b is eliminated, and a run-out of the rotation of the spindle 2 is kept to a minimum.
When the drive source (not shown) is activated, the pulley is rotated via the belt 8 so that the spindle 2 which is integrated with the pulley 4 rotates and the magnetic disc is rotated.
In this type of conventional disc driving unit, however, because the bearings 3a and 3b support a shaft 2b with a diameter smaller than the spindle 2, if there is any play in the bearings 3a and 3b, this play increases on the spindle 2 during rotation. Consequently, it is not possible to provide high accuracy or high planarity in the rotation of the spindle.
To prevent the play, it is necessary to mount the bearings and other components with an extremely small mounting error. Consequently, all components must have high accuracy.
Moreover, conventional disc driving units have a large number of components so that each component requires much greater accuracy, and a larger number of assembly steps are also required. This meant that conventional disc driving units had the disadvantage of high manufacturing costs.
Furthermore, since an overall thickness of an unit is determined by the thickness of components, an arrangement like the conventional unit having a large number of components has the disadvantage that it is extremely difficult to keep the unit slim.
Furthermore, the bearings 3a and 3b are disposed underneath the spindle 2 so that the overall height of the unit is increased, further hindering a slim design.